4MA1/1HR Jun 2018, Question 5: Prime Numbers
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1HR (Higher) · Calculator · 2 marks
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The question, in short
Given E = n² + n + 5, decide whether Ali is right that E is prime for every whole number n, justifying the conclusion.
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Solution · 2 marks
- 1n = 1, 2, 3 give E = 7, 11, 17, all prime
- 2Try n = 4: E = 16 + 4 + 5 = 25
- 3No, because when n = 4, E = 25, which is not a prime number
AnswerNo, because when n = 4, E = 25, which is not a prime number
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